In a magnetooptical disk memory system data is written to a magnetic disk by means of a magnetic write transducer, for example, and read by an optoelectronic device that includes a more or less complicated optical focusing device in cooperation with a photoelectronic transducer and a circuit for amplifying signals provided by the transducer. Given the rapid rate of technological evolution, there is a tendency to use such memory systems because they make it possible to obtain radial densities on the order of several thousand tracks per centimeter, and longitudinal densities on the order of 10,000 information bits per centimeter.
The operation of such systems is based on a magnetooptical effect which involves the interaction of linearly polarized light with the magnetic state of a region of the recording layer of a magnetooptical disk. French Patent 2,514,913, corresponding to U.S. Pat. No. 4,510,544, and filed by Compagnie Internationale pour l'Informatique CII HONEYWELL BULL, provides more complete details on the magnetooptical effect. French Patent Application 87.13738, corresponding to U.S. patent application Ser. No. 253,041, filed on Oct. 5, 1987 by Societe BULL S. A., and entitled "Controlled Device for Optical Reading and Magnetic Writing on Data Storage Media," and French Patent Application 87.13739, corresponding to U.S. patent application Ser. No. 253,038, filed on Oct. 5, 1987 by Societe BULL S. A., and entitled "Device for Optical Reading and Magnetic Writing on a Data Storage Medium", describe devices for optical reading and magnetic writing of data on a magnetooptical disk, comprising a magnetic transducer for writing the data on the medium, the transducer being mounted on a skate for flying above the medium, and an optoelectronic device, most of which is mounted on the skate. The skate flies above the magnetooptical disk at a distance of several tenths of a micron. Magnetooptical disks are now well known. One such disk is described in French Patent Application 87.18355, corresponding U.S. patent application Ser. No. 291,142, filed on Dec. 30, 1987 by Societe BULL S. A., and entitled "Magnetooptical Recording Medium Resistant to Corrosion in a Humid Atmosphere." A magnetooptical disk of this kind includes a substrate upon which a first dielectric layer (for example, composed of alumina or aluminum nitride) is deposited, upon which a magnetooptical recording layer is then deposited. The recording layer is composed of an alloy including one or more metals in the first transition series (Fe, Co, Cr, Ni, Mn) and one or more metals in the heavy rare earth group, such as terbium, gadolinium, or dysprosium. A second dielectric layer is deposited on the magnetooptical recording layer. This layer is then covered with a layer of an oxide of silicon (either the monoxide or the dioxide), which protects the second dielectric layer and the magnetooptioal recording layer from mechanical impact and corrosion, especially in damp atmospheres.
It is extremely difficult for a skate such as the one described above to fly over a magnetooptical disk of this kind. To overcome this difficulty, it is first necessary to deposit a lubricating layer thereon. Lubricating layers of this kind have been used for a long time to coat classical magnetic disks; this type of disk is written to and read from by means of magnetic recording and reading transducers. They are usually composed of silicone or lubricating layers that contain carbon. Layers of this kind have been found to be unusable for magnetooptical disks coated with silicon oxide because the silicone lubricating layers do not allow a skate to fly close enough to the surface of the disk, and furthermore, layers that contain carbon are not transparent to light and therefore do not allow optical reading of information stored on the magnetooptical disk.
Products for coating metallic items can also be used in conjunction with magnetooptical disks that include a protective layer of silicon oxide to provide protection from oxidation as well as lubrication. This type of coating allows a skate, including a magnetic write transducer and an optoelectronic read device, to fly over the surface of a disk. This type of product is sold in the form of an aerosol bomb. It consists of a complex mixture of a Freon-based carrier gas, a mixture of solvents of the toluene and polychloroethylene type, and monomeric oxyhydrocarbon elements. It will be referred to hereinbelow by the term "lubricant." It is manufactured and sold, for example, by Dow Corning GmbH of Munich, in the Federal Republic of Germany, under the commercial name Molykote (a registered trademark of Dow Corning Corporation), and is one of a class of "metal protectors."